Modular measuring devices in the sense of the present invention are measuring devices with a sensor module and at least one superordinated module, for example, a measurement transmitter module, wherein the sensor module is coupled with the superordinated module via an interface. An example of a modular measuring device is, for example, a pH measuring device, in which the sensor module includes a pH electrode, especially in the form a single-rod measuring chain, wherein the sensor module is connected to a measurement transmitter module, which conditions a signal of the sensor module and transmits a signal corresponding to the measured value to a superordinated unit, for example, a control system.
The Endress+Hauser manufactures and sells modular pH measuring devices, in which the sensor module is connected via an interface, in the form an inductively coupling, pluggable, connector coupling, to the superordinated module, wherein the measurement transmitter module is associated with a primary side, plug connector element and the sensor module with a secondary side, plug connector element.
The fundamental principle of this interface is described in European Patent 1 206 012 B1. In accordance therewith, the energy supply of the sensor module and the data exchange between the sensor module and the measurement transmitter module occur via the inductive, pluggable, connector coupling. An inductively coupling, pluggable, connector coupling implements the supply of a consumer, e.g. a sensor module, by means of an energy signal, for example, an AC signal. The transmission of data, thus measurement data, or configuration and parameter data, can occur through modulation of the energy signal, for example, wherein the transmission of data by the energy receiving (secondary side) plug connector element from the energy dispensing (primary side) plug connector element can occur through load modulation of the energy signal. For the separating of data and energy, corresponding demodulators are usually provided. Details for this are disclosed in Patent DE 197 19 730 C1, for example. Inductively coupling sensor modules according to the state of the art have the following circuit parts: Voltage supply including a secondary coil, modulator, demodulator, microcontroller, external memory elements (e.g. EEPROM), analog amplifier, and analog-digital converter.
All of the circuit parts named above are used to ascertain, to handle, and on request, transfer the measured value to a superordinated module via the inductively coupling, pluggable, connector coupling. Furthermore, measuring device adjustment values, calibration values, operating hours, etc. are stored in the microcontroller or in the external memory element. In the course of its life, a sensor module stores a relatively large amount of data. This data can be accessed, depending on need, by the superordinated module, whether it is a measurement transmitter or an interface to a process control system.
However, it is to be taken into consideration that for the communication of the named data between measurement transmitter and sensor module, a communication protocol is required. This must be carried out by the sensor completely in one protocol stack. This requires memory capacity and corresponding hardware in the microcontroller. Furthermore, a demodulator, which demodulates the queries of the measurement transmitter and makes them accessible to the microcontroller, is necessary.
For managing and performing the named tasks of the sensor module, a microcontroller is necessary, which implements the recording of the measured value, communication and data storage. This requires a sufficient number of I/O pins, a high powered CPU and a large amount of program memory (flash) and working memory RAM.
The external or internal memory elements of such a sensor module are sized for the longest expected period of use of the sensor module. If the sensor modules are applied at measuring points characterized by a high loading of the sensor module, because of aggressive media, for example, then the life expectancy shrinks significantly and the sensor module has more memory available than it can ever use. Thus, then, the available memory capacity is disposed of along with the sensor module.
Of course, the microcontroller is also disposed of along with the sensor module.
The purchase and disposal of short lived sensor modules, for example, pH sensors with pH glass electrode, lead to unnecessarily high costs.